From: slemieux.tyco@gmail.com (Sylvain Lemieux)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: dts: lpc32xx: set pwm1 & pwm2 default clock rate
Date: Wed, 05 Oct 2016 10:11:19 -0400 [thread overview]
Message-ID: <1475676679.23405.15.camel@localhost> (raw)
In-Reply-To: <1443ec62-4936-c70a-b323-6980a9240a1e@mleia.com>
Hi Vladimir,
On Wed, 2016-10-05 at 05:08 +0300, Vladimir Zapolskiy wrote:
> Hi Sylvain,
>
> On 26.09.2016 21:54, Sylvain Lemieux wrote:
> > From: Sylvain Lemieux <slemieux@tycoint.com>
> >
> > Probably most of NXP LPC32xx boards have 13MHz main oscillator
> > and therefore for HCLK PLL and ARM core clock rate default
> > hardware setting of 16 * 13MHz = 208MHz and the AHB bus clock
> > rate of 208MHz / 2 = 104MHz.
> >
> > The change explicitly defines the peripheral PWM1/PWM2 default
> > clock output rate of 104MHz. If needed it can be redefined
> > in a board DTS file.
> >
> > Signed-off-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
> > ---
> > Note:
> > * There is a dependency on the following patch:
> > "ARM: dts: lpc32xx: set default parent clock for pwm1 & pwm2"
> > http://www.spinics.net/lists/arm-kernel/msg530277.html
> > * This patch should be apply after
> > "ARM: dts: lpc32xx: add pwm-cells to base dts file"
> > http://www.spinics.net/lists/arm-kernel/msg534050.html
> > - There is no dependency between the patches.
> >
> > arch/arm/boot/dts/lpc32xx.dtsi | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arm/boot/dts/lpc32xx.dtsi b/arch/arm/boot/dts/lpc32xx.dtsi
> > index c031c94..d669200 100644
> > --- a/arch/arm/boot/dts/lpc32xx.dtsi
> > +++ b/arch/arm/boot/dts/lpc32xx.dtsi
> > @@ -471,6 +471,7 @@
> > clocks = <&clk LPC32XX_CLK_PWM1>;
> > assigned-clocks = <&clk LPC32XX_CLK_PWM1>;
> > assigned-clock-parents = <&clk LPC32XX_CLK_PERIPH>;
> > + assigned-clock-rates = <104000000>;
>
> PWM controller clock source can be 32KHz or CLK_PERIPH, the latter is
> equal either to SYSCLK or HCLK PLL divided by HCLKDIV_CTRL[6:2].
>
> Do you set the divider to 1? If yes, then I would say
>
> 1) this is very specific to your board, generally CLK_PERIPH
> is set to be about 10-13MHz,
> 2) HCLKDIV or PERIPH clock configuration shall not be done in pwm device node.
>
> 104MHz is too high value to be set by default for PWM clock.
>
This is a good catch; it was an error on my side.
The purpose of the patch was to setup the output of the
PWM clock to the default CLK_PERIPH value (13325000).
This change does not modify the HCLKDIV or the PERIPH clock.
I can submit a version 2 with the proper value and update
the patch description to list the default peripheral clock
setup of 13MHz.
This change is adding a default value for the PWM clock
(setup to CLK_PERIPH) to the PWM device node, allowing the
board specific DTS to only enable the PWM to get it work.
If the PWM clock output is not setup with a default value,
only enabling the PWM in the board specific DTS file is not
enough; the PWM divider will keep the default value of zero
(i.e. PWM clock off).
> --
> With best wishes,
> Vladimir
Sylvain
next prev parent reply other threads:[~2016-10-05 14:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-26 18:54 [PATCH] ARM: dts: lpc32xx: set pwm1 & pwm2 default clock rate Sylvain Lemieux
2016-10-05 2:08 ` Vladimir Zapolskiy
2016-10-05 14:11 ` Sylvain Lemieux [this message]
2016-10-11 15:51 ` Sylvain Lemieux
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